Antenna design always requires a trade-off. Usually a larger and more expensive antenna will provide better operational performance. An antenna can be made smaller at the expense of higher cost, or at the expense of decreased performance. The present invention provides a small and potentially inexpensive antenna with excellent performance.
The specific application intended for the antenna of the present invention is the so-called Advanced Communication Technology satellite ("ACTS") and Advanced Mobile Terminal ("AMT") made by NASA's Jet Propulsion Laboratory. This system is intended to provide voice data and video communication from a mobile vehicle via a geostationary ACTS satellite operating using the K and Ka band frequencies. A critical component of the AMT is its antenna system which must establish and maintain the basic RF link with the satellite.
The ACTS/AMT system will initially provide a demonstration of voice, fax and compressed video transmitted from a van or car travelling along roads and highways to a geostationary satellite. A two-way communication is envisioned between the vehicle and the first location, to the ACTS satellite and to a base station in a second location. The antenna must have a sufficiently wide elevation coverage so that only azimuthal tracking is required.
The specific requirements of the system require a low-profile, compact antenna array with approximately 22 dBi gain that receives vertical polarization at 20 GHz and transmits horizontal polarization at 30 GHz.
The antenna of the present invention provides a novel approach to meeting these requirements by using a multi-layered/interleaved array antenna of microstrips, slots and dipoles. A first planar array includes series-fed linear arrays of slots and a second planar array includes series-fed linear arrays of dipoles. Each of the arrays is formed of elements that are transversely coupled to a microstrip transmission line. The dipole and slot radiating elements have similar radiation patterns but radiate orthogonal polarizations.
More specifically, the antenna of the present invention includes a first layer including a receive array and a second layer including a transmit array. Each of the arrays include a plurality of subarrays; each subarray formed from a layer of separated antenna elements and a microstrip transmission line layer coupling together the antenna elements. The subarrays collectively form a plane of series-fed-type linear arrays. Different aspects of the elements relative to the microstrip transmission line can be modified in order to change various characteristics of the antenna. According to one particular aspect of the antenna, one of the layers is used as the ground plane for the other of the layers.